pigment particle composition, its method of manufacture and its use

ABSTRACT

A pigment particle composition which comprises calcium carbonate particles and pigment particles, its method of manufacture and its use. According to the present invention, the calcium carbonate particles are carbonated so that they bind to each other, in which case calcium carbonate structures are generated, which comprise pigment particles and which form essentially opaque and stable pigment-calcium carbonate aggregates. It is possible to manufacture the composition by atomizing calcium hydroxide-bearing pigment slurry into a carbon dioxide-bearing gas, in which case the calcium hydroxide is carbonated in order to precipitate the calcium hydroxide particles to be attached to each other and the carbonation is continued until essentially all of the calcium hydroxide has been converted into calcium carbonate. The composition is suitable for use, among others, in paints, coating materials, fillers, polymers and printing inks.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is entitled to the benefit of and incorporates byreference essential subject matter disclosed in International PatentApplication No. PCT/FI2009/050187 filed on Mar. 9, 2009 and FinnishPatent Application No. 20085213 filed Mar. 7, 2008.

FIELD OF THE INVENTION

The present invention relates to a pigment particle composition.

BACKGROUND OF THE INVENTION

A composition like this generally comprises calcium carbonate particlesand pigment particles.

The present invention also relates to a method of manufacturing apigment particle composition, and also to paint, coating material,filling material, polymer and printing ink compositions.

Because of its high refractive index, titanium dioxide is used as alight-scattering white pigment in paints, printing inks and many othercoating compositions, and also in filling materials.

Titanium dioxide is expensive and difficult to recycle. In order toreduce the quantities required, titanium dioxide is typically mixed withextenders, but it is necessary to keep the amounts of extender verysmall, otherwise the optical properties which are achieved with titaniumdioxide are lost, especially the opacity achieved, which is criticallyimportant in particular for paints and coating compositions, and forfilling materials, too.

SUMMARY OF THE INVENTION

It is an aim of the present invention to eliminate the disadvantagesassociated with the known technology and to generate completely newpigment compositions, in which it is possible to reduce the amount ofthe light-scattering pigment, without degrading the achieved opticalproperties, particularly the opacity.

The present invention is based on the idea that a shell which comprisesprecipitated calcium carbonate particles is formed around the pigmentparticles, which shell at least partly encases one or several pigmentparticles.

In this case, according to the present invention, the calcium carbonateparticles are at least mainly carbonated so that they bind to each otherto form calcium carbonate structures. These structures comprise one orseveral particles, but generally only one or two pigment particles,which together with the calcium carbonate form essentially opaque andstable pigment-calcium carbonate aggregates.

It is possible to manufacture such compositions for instance

-   -   by atomizing a calcium hydroxide-bearing aqueous slurry which        comprises pigment particles into a carbon dioxide-bearing gas,        in order to carbonate the calcium hydroxide;    -   by choosing the amount of the calcium hydroxide in the aqueous        slurry in such a way that the calcium carbonate percentage in        the pigment composition is equivalent to a predefined weight        percentage;    -   by carbonating the calcium hydroxide in order to carbonate the        calcium carbonate particles to be attached to each other; and    -   by continuing the carbonation until essentially all the calcium        hydroxide has been converted into calcium carbonate.

It is possible to use the composition according to the present inventionas a pigment in paints, in coating material compositions in paper orcardboard, in filling material compositions in paper or cardboard, inplastics or in printing inks.

More specifically, the composition according to the present invention issuch that at least part of the calcium carbonate particles arecarbonated so that they bind to each other to form calcium carbonatestructures which comprise at least one pigment particle and whichcalcium carbonate structures, together with the pigment particles, formessentially opaque and stable pigment-calcium carbonate aggregates.

The method according to the present invention is, in turn, characterizedin that the calcium dioxide-bearing aqueous slurry which comprisespigment particles is atomized into calcium dioxide-bearing gas in orderto carbonate the calcium hydroxide, and in turn to generate a pigmentcomposition which comprises calcium carbonate, the amount of calciumhydroxide in the aqueous slurry is chosen in such a way that thepercentage of calcium carbonate in the pigment composition is equivalentto a predefined weight percentage, and the calcium hydroxide iscarbonated in order to precipitate the calcium carbonate particles whichare to be attached to each other, and the carbonation is continued untilessentially all of the calcium hydroxide has been converted into calciumcarbonate, and the paint, coating material, filling material, polymerand printing ink compositions according to the present invention arecharacterized in that at least 1 weight-% of the pigment comprisescompositions as stated above.

The usage according to the present invention is as a pigment in paint,in coating material composition in paper or cardboard, in fillercomposition in paper or cardboard, in plastic or in printing ink.

Considerable advantages can be achieved with the present invention.Thus, an excellent opacity is achieved by means of this pigmentcomposition, and also it is possible to use it as a substitute for morethan 50 weight-% of the white pigment of the titanium dioxide in forinstance a paint composition.

We have discovered that when the pigment particles are titanium dioxide,the opacity which can be achieved by applying the calcium carbonatemodification is, already at weight ratios of 10:90 . . . 30:70 betweentitanium dioxide and calcium carbonate, at least nearly as good as with100% titanium dioxide, in an application where part or all of thetitanium dioxide is substituted by calcium carbonate.

The excellent properties of the compositions according to the presentinvention are mainly a result of the fact that the pigment particles areseparated from each other by the calcium carbonate structures in such away that the distance between them is at least approximately 60 nm,preferably at least approximately 100 nm, most suitably at leastapproximately 120 nm.

Because the price of calcium carbonate is substantially less than thatof titanium dioxide or that of many other light-scattering pigmentparticles, the present invention offers a significant reduction inpigment costs.

With particular regard to titanium dioxide, it is important to note thatin the market of white covering pigments there is no real substitute forit (i.e. titanium dioxide) However, the drawback with titanium dioxideis its tendency to agglomerate, in which case its light-scattering powerdrops significantly. Another advantage of the present invention is thatwe have now found a way of efficiently utilizing the high refractiveindex (light-scattering index) of titanium. In the manufacturing of theshell according to the present invention it is possible to use verycost-effective materials, namely calcium oxide/calcium hydroxide andcarbon dioxide to substitute for the expensive titanium dioxide.

Another problem associated with titanium dioxide in paper and cardboardapplications is that its retention quality is often poor, whichcharacteristic is improved by using the product according to the presentinvention, because this product has a larger particle size and a lowerdensity than titanium dioxide. Larger and lighter particles are morereadily retained in the fibre network, and are not removed along withthe water (mechanical retention).

The manufacturing method is simple and industrially useful: it is veryfast, and being a carbonating process it is very efficient. Thegeneration of the carbonate shell takes place in-situ, in which case aseparate manufacturing of PCC is not needed.

The method can be applied at an industrial scale. According to apreferred embodiment of the present invention, the manufacturing of apigment composition is carried out continuously.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention is examined more closely withthe help of a detailed explanation and the accompanying drawings, whereFIGS. 1 a and 1 b are electron microscopic pictures of a calciumcarbonate-pigment particle composition manufactured according to thepresent invention;

FIG. 2 shows schematically, as an example, a vertical cross-section ofone of the precipitation reactors according to the present invention;

FIG. 3 shows schematically, as an example, a horizontal cross-section ofa atomizer which is fitted into the precipitation reactor according toFIG. 2;

FIG. 4 shows schematically, as an example, a vertical cross-section ofthe second precipitation reactor according to the present invention;

FIG. 5 shows schematically, as an example, a atomizer of theprecipitation reactor according to FIG. 4; and

FIG. 6 shows schematically, as an example, a vertical cross-section ofthe group of the precipitation reactors according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 a and 1 b show electron microscopic pictures of a calciumcarbonate-pigment product, which is manufactured according to thepresent invention and which comprises titanium dioxide particles encasedby calcium carbonate particles. The calcium carbonate comprisesparticles which are manufactured from calcium hydroxide by a process ofcarbonation (i.e. precipitated calcium carbonate, PCC). FIGS. 1 a and 1b illustrate how, according to an embodiment of the present invention,the calcium carbonate particles are typically carbonated in order toattach them to each other in such a way that they form a shell which atleast partly encases the said, at least one, pigment particle. On thebasis of analyses, the thickness of the shell is on average at leastapproximately 30 nm, especially at least approximately 50 nm, mostsuitably approximately 60-500 nm.

On the basis of the pictures, the calcium carbonate particles are mainlynon-spherical in form. Typically, their external form is at least mainlyrhombic or rhombohedric.

The particles are crystalline and their crystal form is mainly calciteor—to a lesser degree—aragonite.

FIGS. 1 a and 1 b show that the calcium carbonate particles form apolynuclear calcium carbonate structure, to which a pigment particle isattached. Our tests have shown that the calcium carbonate particles andthe pigment particles, which in this picture are titanium dioxideparticles, are strongly attached to each other. The majority of thecalcium carbonate particles (i.e. more than 50%, typically even morethan 90 or 95%) remain attached to the calcium carbonate crystals bothin the dry pigment composition and in the aqueous slurry of the pigmentcomposition.

The attribute “stable”, which is used for the calcium carbonate-pigmentaggregate, means that a considerable percentage (at least approximately50 weight-%, especially approximately 75 weight-%, most suitably atleast approximately 90 weight-%) of the pigment particles which are partof the aggregate remain attached to the calcium carbonate particles eventhough the calcium carbonate-pigment aggregates are dispersed in waterand then dried or—vice versa—even though they are dried to powder formand then dispersed in water.

Opaqueness means that the calcium carbonate-pigment aggregation gives,as a pigment, a good opacity to that intermediate agent into which it ismixed when substituting for part or all of the pigment, in theembodiment. Typically, this opacity is of the same magnitude (with avariation range of approximately 10%) as the associated pigment. Anexcellent opacity is mainly a result of the above-mentioned fact, i.e.that it is possible to keep the pigment particles, which are coveredwith the shells, at such a distance from each other that it producesoptimal opacity, and that the retention of those particles is good andthey are evenly distributed in the intermediate agent.

The shell which is formed of the calcium carbonate particles encases,partly or totally, approximately 1-20, especially approximately 1-10,preferably 1-3 pigment particles. In the figure it is difficult todistinguish the individual titanium dioxide particles from the calciumcarbonate because the former are completely encased by the latter.

The calcium carbonate structure is formed of calcium carbonateparticles, the original size of which, before they are carbonated inorder to attach them to other particles, is on average approximately20-250 nm. When the calcium carbonate particles coalesce, they form anessentially continuous surface.

The weight ratio between the pigment particles and the calcium carbonateparticles is approximately 90:10 . . . 5:95, preferably approximately60:40 . . . 5:95, and especially approximately 40:60 . . . 10:90. Thecomposition according to FIGS. 1 a and 1 b represents a case in whichthe amount of titanium dioxide is on average approximately 18 weight-%and the amount of calcium carbonate is on average approximately 82weight-% of the total amount of the pigment and calcium carbonate.

In the manufacturing, the weight ratio between the light-scatteringpigment and the calcium carbonate is adjusted to the desired ratio bychoosing the amounts of the calcium hydroxide and calcium carbonate inthe aqueous slurry to be carbonated in such a way that the calciumcarbonate percentage in the final pigment composition corresponds to apredefined weight percentage.

The pigment compositions may comprise, besides the pigment particles andthe calcium carbonate particles, also other elements, such asdispersants, surface modifying agents and stabilising agents or mixturesthereof. However, the total amount of these is at maximum approximately20 weight-% of the total weight of the composition, typically below 10%.

The composition according to the present invention is typicallymanufactured

-   -   by atomizing a calcium hydroxide-bearing aqueous slurry which        comprises pigment particles into a carbon dioxide-bearing gas,        in order to carbonate the calcium hydroxide to generate calcium        carbonate, and in turn to generate a pigment composition, and    -   by choosing the amount of the calcium hydroxide in the aqueous        slurry in such a way that the percentage of the calcium        carbonate in the pigment composition corresponds to a predefined        weight percentage.

In this method, calcium carbonate particles are precipitated fromcalcium hydroxide and carbon dioxide in such a way that calciumcarbonate particles adhere to the surface of pigment particles and arecarbonated in order to attach them to other calcium carbonate particles,in which case essentially opaque and stable pigment-calcium carbonateaggregates are formed, which are at least partly covered with calciumcarbonate particles.

Preferably, the calcium hydroxide-bearing aqueous slurry which comprisestitanium dioxide particles is at least essentially fibre free, in whichcase all of the calcium hydroxide to be precipitated is available forthe coating of the pigment particles.

The method makes it possible to adjust the weight ratio between thepigment particles and the calcium carbonate to the desired ratio bychoosing the amounts of the calcium hydroxide and the calcium carbonatein the aqueous slurry in such a way that the percentage of the calciumcarbonate in the final pigment composition corresponds to a predefinedweight percentage.

Typically, the calcium hydroxide-bearing aqueous slurry which comprisespigment particles is led through a high energy mixing zone, in whichzone the aqueous slurry is broken up into drops or even into nebulousdrops, and then dripped into a carbon dioxide-bearing gas. Thecarbonation is continued until essentially all of the calcium hydroxidehas been transformed into calcium carbonate.

FIGS. 1 a and 1 b show calcium carbonate compositions which comprisetitanium dioxide. The crystalline form of the titanium dioxide, in turn,can be rutile or anatase. However, the solution according to the presentinvention is also suitable for other light-scattering and/or absorbingpigments, such as aluminium hydroxide, barium sulphate, kaolin, gypsum,ground or precipitated calcium carbonate, chalk or mixtures thereof, andalso for organic pigment materials, such as plastic pigments and furnaceblack and mixtures thereof.

In the method according to the present invention, calciumhydroxide-bearing aqueous slurry which comprises pigment particles isdripped into a carbon dioxide-bearing gas in order to carbonate thecalcium hydroxide with the purpose of forming a pigment compositionwhich comprises calcium carbonate. The method is preferably carried outin a surplus of carbon dioxide, in which case the formation of calciumcarbonate is limited only by the amount of the calcium hydroxide whichis fed into the system. In these conditions the carbonation is typicallycontinued until the pH value of the pigment slurry is essentiallyneutral. There is no need to add any acid.

The processing along with the process equipment are described below indetail with the help of FIGS. 2-6. In general, it can be seen that it isadvantageous to carry out the carbonation in several stages. In thiscase, the aqueous slurry, which is generated by the atomizing of thecalcium hydroxide-bearing aqueous slurry into carbon dioxide gas inconjunction with the carbonation, is recovered and is most suitablybrought to further carbonation.

According to an embodiment, the aqueous slurry is further carbonated byatomizing it once more into carbon dioxide gas. In another embodiment,it is further carbonated by bubbling carbon dioxide gas into the slurry.

Typically, carbonation is carried out continuously in such a way thatthe aqueous slurry undergoes at least one atomizing. Thelight-scattering and calcium hydroxide-bearing aqueous slurry whichcomprises pigment particles is then led through a high energy mixingzone, in which zone the aqueous slurry is broken up into drops or eveninto nebulous drops, and then dripped into a carbon dioxide-bearing gas.If necessary, dispersants, surface modifying agents or stabilisingagents or mixtures thereof are added to the pigment composition to bemanufactured during or after manufacturing.

Essentially, all of the calcium hydroxide-bearing aqueous slurry can beadded to the carbonation together with the pigment particles. However,it is also possible to introduce the calcium hydroxide-bearing aqueousslurry into the carbonation gradually and in several batches, in whichcase most suitably at least part of the calcium hydroxide-bearingaqueous slurry is free of pigments when it is fed into the carbonation.

According to an embodiment, pigment is added little by little andpossibly separate from the calcium hydroxide.

The method is typically carried out at temperatures of approximately30-100° C., especially approximately 50-80° C.

In the following, the applications shown in the drawings will beexamined more closely.

FIG. 2 shows a continuously working precipitation reactor (10),according to the present invention, which reactor comprises aprecipitation vessel (12), a atomizer (14) fitted into the precipitationvessel, a feed pipe (16) for the calcium hydroxide-bearing aqueousslurry which comprises titanium dioxide particles, an inlet pipe (18)for the precipitating gas, and a discharge pipe (20) for the treatedpigment composition. In addition, the equipment comprises an actuator(22), including the bearing and sealing assembly (24) which lie betweenthe actuator (22) and the atomizer (14).

The atomizer (14), a horizontal section of which is shown in FIG. 3, isa through-flow mixer which has 6 coaxial rings 26, 26′, 26″, 28′, 28′,28″, equipped with blades 26 a, 26′a, 26″a, 28 a, 28′a, 28″a. In thisdevice (14), the calcium hydroxide-bearing aqueous slurry whichcomprises titanium dioxide particles is dripped to form small particles,liquid drops and/or particles of solids. The dwell time in the atomizeris short, <10 seconds, typically <2 seconds, most typically even lessthan 1 second.

As the arrows in FIG. 3 indicate, one set of rings, 26, 26′, 26″, of theatomizer functions as rotors which, in the case of FIG. 3, rotatecounterclockwise. The other set of rings, 28, 28′, 28″, placedalternately between the rings in the first set, also function as rotors;however, they rotate clockwise in this case. Blades 26 a, 26 a′, 26 a″and 28 a, 28 a′, 28 a″, which are mounted on both sets of rings,encounter the pigment composition travelling outwards and radiallythrough the device, resulting in the composition being exposed torecurrent impacts and double impacts. It is also possible to drip thecalcium hydroxide-bearing aqueous slurry which comprises pigmentparticles, by using equipment having fixed rings, i.e. stators, betweeneach set of clockwise-rotating rings and also between each set ofcounterclockwise-rotating rings.

The calcium hydroxide-bearing aqueous slurry which comprises titaniumdioxide particles is fed through a pipe (16) to the centre (30) of theatomizer, from where it travels, as a result of the movement of theblades of the rotors and the difference in pressure created between thecentre and the periphery of the device, radially outwards, towards theopen outer edge (32) of the outer ring (28″). This aqueous slurry can befed into the device (14) in between the rings as well, when necessary.If desired, it is also possible to feed the titanium dioxide particlesand the calcium hydroxide-bearing aqueous slurry into the atomizer (14)through separate pipes, in which case the formation of the calciumhydroxide-bearing aqueous slurry which comprises titanium dioxideparticles occurs no earlier than at this point.

The impacts and double impacts, the shear forces, the turbulence and thepulses of both underpressure and overpressure which are generated by themovement of the rotor blades rotating in opposite directions, drip thecalcium hydroxide-bearing aqueous slurry which comprises titaniumdioxide particles into fine fractions, liquid drops and particles ofsolids. It is also possible to generate the same effect by using rotorswhich rotate in the same direction but at greatly differing speeds, orby using a rotor-stator combination.

In the solution, according to the present invention, shown in FIGS. 2and 3, the precipitating gas is directed through the pipe (18) to thecentre (30) of the rings of the atomizer. From this centre, the gasflows radially outwards generating, both in the atomizer and in theprecipitation vessel (12) around it, a gaseous space (34) comprising theprecipitating gas. The gas is discharged through the pipe (21) locatedon the top section of the precipitation reactor. If desired, it ispossible to feed the precipitating gas to the rings and/or in betweenthe rings of the atomizer, too. The precipitation reactions may alreadybegin in the gaseous space of the atomizer.

When treated in the atomizer (14), the calcium hydroxide-bearing aqueousslurry which comprises titanium dioxide particles generates fine dropsand particles, which are dispersed from the device (14) into thesurrounding section (34′) of the gaseous space. The fine drops andparticles are forcibly ejected from the atomizer, mainly from its outerring area, as a nebulous flow (36). Following ejection from theatomizer, the precipitation reactions may continue for a relatively longtime while the fine drops and particles disperse widely in theprecipitation vessel. The treated fibre composition descends into thepool at the bottom of the precipitation vessel, and is discharged fromthe vessel through a pipe (20).

A suitable size, shape, width and height of the precipitation vessel(12) may be selected to ensure that the drops and particles, which areejected from the atomizer, remain in the gaseous space (34′) of theprecipitation vessel for an optimal dwell time. For example, increasingthe height of the precipitation vessel (12), making it tower-like,increases the dwell time of the fibre composition.

Processes in the precipitation reactor (10) may also be regulated byadjusting, for example, the number of rings, the distance between therings, the distance between the blades on each ring, and the bladedimension and position, in the atomizer.

The pigment composition which is discharged through the bottom of theprecipitation vessel (12) can be re-circulated back to the sameprecipitation reactor, or be fed to another reactor, to finish thetreatment.

FIGS. 4 and 5, which illustrate another precipitation reactor accordingto the present invention with its atomizer, use the same referencenumbers as presented in FIGS. 1 and 2, when applicable. According to theinvention, another precipitation reactor (10), presented in FIG. 4,differs from the device presented in FIGS. 2 and 3 mainly in that thereactor comprises a atomizer (14) equipped with a closed outer ring, andin that the precipitation reactor does not include a separateprecipitation area extending beyond the atomizer. The solution presentedin FIGS. 4 and 5 is suitable to be used, for example, when theprecipitation reactions are assumed to be completed in the desiredmanner already in the gaseous space of the atomizer.

In the atomizer presented in FIGS. 4 and 5, the outermost ring (28′) issurrounded by a housing (40) which seals the ring. The housing comprisesa discharge opening (42) for discharging the treated fibre compositionfrom the device (14). The treated fibre composition may be directed fromthe discharge opening (42) through a pipe for further treatment orfurther processing. As shown in FIG. 4, the material discharged from theprecipitation reactor may also be re-circulated back to the same reactoror directed to another reactor, to finish the carbonation.

Two or more of both types of precipitation reactors presented in FIGS. 2and 4 can be arranged in a sequential series. FIG. 6 illustrates a groupof three precipitation reactors arranged in a sequential series. Thefirst reactor is of the type presented in FIG. 4 and the next tworeactors are of the type presented in FIG. 2. When applicable, thereference numbers are the same as in the previous diagrams.

FIG. 6 illustrates three precipitation reactors 10, 10′ and 10″, wherethe calcium hydroxide-bearing aqueous slurry which comprises titaniumdioxide particles is treated with CO₂ gas for carbonating Ca²⁺ ions,i.e. to precipitate CaCO₃. The calcium hydroxide-bearing aqueous slurrywhich comprises titanium dioxide particles is directed through a pipe atthe top into the first precipitation reactor (10), into which carbondioxide-bearing gas, too, is directed via a pipe (18). The partlycarbonated pigment composition is directed via the break tank (48) intothe second precipitation reactor (10′). Into the aqueous slurry to betreated, calcium hydroxide which is to be precipitated may be addedthrough the pipe (52) as well, after the first precipitation reactor.

From the break tank (48), the partly treated aqueous slurry, whichcomprises pigment composition and unprecipitated calcium hydroxide, isdirected through the discharge pipe to the feed pipe (16) of the secondreactor (10′), and is thereafter directed via the bottom to the atomizer(14) of the second precipitation reactor. The precipitating gas (18′),typically carbon dioxide, is directed together with the pigmentcomposition to the device (14). Correspondingly, the pigment compositionwhich has been treated in the second reactor (10′) and the aqueousslurry which comprises unprecipitated calcium hydroxide are directedthrough the discharge pipe (20′) to the feed pipe (16′) of the thirdreactor (10″). From the bottom of the third reactor (10″), mainlypreviously treated pigment composition, in which the weight ratiobetween the titanium dioxide and the calcium carbonate is predetermined,is removed by way of a pipe (20″).

It is possible to add calcium hydroxide or calcium carbonate at anystage of the process, before the finishing of the pigment composition inthe last reactor. The average size of the bound calcium carbonateparticles can be affected by additions of calcium hydroxide. Titaniumdioxide, too, can be added at any stage of the process, before thefinishing of the pigment composition in the last reactor, in order toachieve a desired weight ratio between the titanium dioxide and thecalcium carbonate.

Carbon dioxide-bearing gas is led to each reactor through the pipes 18,18′, 18″. Carbon dioxide-bearing gas is fed through the feed pipe 18 tothe first reactor 10, which induces precipitation (carbonisation). Thecalcium carbonate particles which are generated precipitate on thetitanium dioxide particles and, to some degree, the calcium carbonateparticles precipitate on each other, too. It is possible to direct thesame or another carbon dioxide-bearing gas to the second and the thirdprecipitation reactors 10′, 10″ through pipes 18′, 18″ in order tocomplete the precipitation reactions (carbonisation). Gas is removedfrom the reactors through discharge pipes 21, 21′, 21″ Typically the gasto be removed comprises steam and carbon dioxide. The gas is directedfor treatment in a gas-washing and cooling device (54). In the device(54), the treated carbon dioxide-bearing gas is re-circulated back tothe precipitation reactors.

The manufactured compositions are suitable for several applications inwhich traditional pigments such as titanium dioxide are used today. Tomention a few examples:

-   -   Paint compositions which comprise pigment and binder, and        conventional manufacturing materials and additives used in        paints    -   Coating material compositions which comprise pigment and binder,        and conventional manufacturing materials and additives used in        coating materials    -   Filler compositions which comprise pigment, and conventional        manufacturing materials and additives used in filler        compositions    -   Polymer compositions which comprise thermoplastic polymer, in        which pigment and possibly conventional manufacturing materials        and additives used in polymer composition, are mixed, and    -   Printing ink compositions which comprise pigment mixed in a        liquid phase, binder and possibly colour pigment and other        manufacturing materials and additives used in printing ink        compositions.

In all of these, at least 1 weight-%, most suitably at least 5 weight-%,especially approximately 20 weight-% of the pigment comprises a calciumcarbonate-pigment aggregate according to any of the applicationsdescribed above.

The following non-limiting examples illustrate the present invention.

Example 1 Manufacturing of a Pigment Particle Composition

Raw Materials Used in the Tests

1. Ca(OH)₂ aqueous slurry, the dry matter content of which wasapproximately 17%, T=60° C.2. Commercial titanium dioxide elutriated in approximately 50% drymatter, T=20° C.3. CO₂ bearing gas, T=20° C.

With the method according to the present invention, a pigment particlecomposition was prepared by feeding a needed amount of Ca(OH)₂ slurryand a titanium dioxide slurry into a group of precipitation reactors,shown in FIG. 6, with the purpose of generating a titanium dioxide/PCCmass ratio of 30/70 after the precipitation. A surplus of carbondioxide-bearing gas, too, was fed into the precipitation reactors. Thetitanium calcium hydroxide-bearing aqueous slurry which comprisestitanium dioxide particles was broken up into small drops in the carbondioxide-bearing gas by directing the slurry through a high energy mixingzone.

The partly treated pigment composition was pumped from the firstprecipitation reactor into the second precipitation reactor and,furthermore, from there into the third precipitation reactor, from whicha pigment particle composition according to the present invention wasobtained, having a dry matter percentage of 24% and at a temperature of65° C. The pH of the pigment composition after the third precipitationreactor was 6.9, i.e. essentially all of the Ca(OH)₂ had beenprecipitated into calcium carbonate. The calcium carbonate percentage ofthe pigment composition was determined by titration. The result was69.9%, as desired.

Example 2

With the method according to the present invention, a pigmentcomposition was prepared in which the mass ratio between the titaniumdioxide and the calcium carbonate was 18/82. The dry matter content ofthe composition was increased to 60% and a dispersant was added into it,thereby obtaining a very fluid pigment slurry. With this product, afully matt and much filled (PVC>70%) primer was prepared in such a waythat no other component was changed, except that 50 parts per weight ofthe titanium dioxide were substituted by an equivalent amount of thepigment composition according to the present invention (calculated asdry per dry).

Titanium dioxide accounted for 8.0 weight-% of the reference paint.

The test point comprised 4.0 weight-% of titanium dioxide and 4.0weight-% of the pigment composition according to the present invention.The covering powers of the paints prepared in this way were measured,and the following results were obtained:

Reference 96.3% Test point 96.2%

Example 3

Water was removed from the pigment composition according to example 1 byusing a centrifuge, and a dispersant was added thereby obtaining a veryfluid pigment slurry, the dry matter content of which was 60%. Thisproduct was used to substitute for titanium dioxide, which is used forcoating cardboard, in such a way that no other component of the coatingpaste was affected. The reference paste comprised 4 parts of titaniumdioxide and 96 parts of ground calcium carbonate. In the test point 1,half of the titanium dioxide and in test point 2, all of the titaniumdioxide was substituted by the pigment composition according to thepresent invention. The paste was applied 12 g/m² on the cardboard. Thelayer of coating was removed from the final cardboard by dissolving andthe opacity of the cardboard was then measured. The following resultswere obtained:

Reference 78.4% Test point 1 78.3% Test point 2 78.6%

Example 4

The titanium dioxide which is used as a filler in paper was substitutedby a pigment composition according to the present invention in such away that no other component which is used in paper production wasmodified As a second reference, some paper was prepared by using amixture of titanium dioxide and scalenohedric commercial PCC as fillers,the ratio being the same as between the titanium dioxide and calciumcarbonate in the product according to the present invention, i.e. 30/70.The grammage of the paper was 60 g/m² and the filler percentage 10%. Theopacity of a paper sheet prepared in this way was measured, and thefollowing results were obtained:

Reference 1 85.5% Reference 2 83.8% Test point 1 85.7%

The present invention is not to be restricted to the explanations andexamples above. Instead, it is intended that the present invention bewidely applied within the limits determined in the claims presentedbelow.

1. A pigment particle composition which comprises calcium carbonateparticles and pigment particles, wherein at least part of the calciumcarbonate particles are carbonated so that they bind to each other toform calcium carbonate structures which comprise at least one pigmentparticle and which calcium carbonate structures, together with thepigment particles, form essentially opaque and stable pigment-calciumcarbonate aggregates.
 2. The composition according to claim 1, whereinthe calcium carbonate particles, which are carbonated so that they bindto each other, form a shell, which at least partly encases the said, atleast one, pigment particle.
 3. The composition according to claim 1,wherein the calcium carbonate particles are mainly non-spherical inform.
 4. The composition according to claim 1 wherein the calciumcarbonate particles form a polynuclear calcium carbonate structure, towhich a pigment particle is attached.
 5. The composition according toclaim 1, wherein the crystalline form of the calcium carbonate particlesis calcite or aragonite.
 6. The composition according to claim 1,wherein the external form of the calcium carbonate particles is at leastmainly rhombic or rhombohedric.
 7. The composition according to claim 1,wherein calcium carbonate crystals are attached to at least themajority, typically to more than 95% of the pigment particles, in such away that in the majority of instances, and typically in more than 95% ofinstances, of the pigment particles, the calcium carbonate crystalsremain attached, both in the dry pigment composition and in the aqueousslurry of the pigment composition.
 8. The composition according to claim1, wherein the shell formed of the calcium carbonate particles encases,partly or totally, approximately 1-20, especially approximately 1-10,preferably 1-3 pigment particles.
 9. The composition according to claim1, wherein the calcium carbonate structure is formed of calciumcarbonate particles, the average size of which is approximately 20-250nm.
 10. The composition according to claim 1, wherein the pigmentcomposition comprises other components, such as dispersants,surface-modifying agents and stabilising agents or mixtures thereof. 11.The composition according to claim 1, wherein the weight ratio betweenthe pigment particles and the calcium carbonate particles isapproximately 90:10 . . . 5:95, preferably approximately 60:40 . . .5:95, and especially approximately 40:60 . . . 10:90.
 12. Thecomposition according to claim 1, wherein it is possible to manufactureit by atomizing a calcium hydroxide-bearing aqueous slurry whichcomprises pigment particles into carbon dioxide-bearing gas, in order tocarbonate the calcium hydroxide to generate calcium carbonate, and inturn to generate a pigment composition, and by choosing the amount ofthe calcium hydroxide in the aqueous slurry in such a way that thepercentage of calcium carbonate in the pigment composition is equivalentto a predefined weight percentage.
 13. The composition according toclaim 1, wherein it is possible to adjust the weight ratio between thepigment particles and the calcium carbonate to the desired ratio bychoosing the amount of the calcium hydroxide and the amount of thecalcium carbonate in the aqueous slurry in such a way that thepercentage of the calcium carbonate in the final pigment compositioncorresponds to a predefined weight percentage.
 14. The compositionaccording to claim 12, wherein the calcium hydroxide-bearing aqueousslurry which comprises pigment particles is directed through a highenergy mixing zone, in which zone the aqueous slurry is broken up intodrops or even into nebulous drops, and then dripped into a carbondioxide-bearing gas.
 15. The composition according to claim 12, whereinthe carbonation reaction is continued until essentially all of thecalcium hydroxide has been converted into calcium carbonate.
 16. Thecomposition according to claim 14, wherein the calcium hydroxide-bearingaqueous slurry of the pigment particles is at least essentially free offibres.
 17. The composition according to claim 1, wherein the pigmentsare light-scattering and/or absorbing pigments, such as titaniumdioxide, aluminium hydroxide, barium sulphate, kaolin, gypsum, ground orprecipitated calcium carbonate, chalk, or mixtures thereof, or organicpigment materials, such as plastic pigments and furnace black, ormixtures thereof.
 18. The composition according to claim 1, wherein thepigment particles are titanium oxide and that the opacity which can beachieved by using this composition is, already at weight ratios of 10:90. . . 30:70 between titanium dioxide and calcium carbonate, at leastnearly as good as with 100% titanium dioxide, in the application wherepart or all of the titanium dioxide is substituted by calcium carbonate.19. The composition according to claim 1, wherein the crystalline formof the titanium dioxide which is used as the pigment particles is rutileor anatase.
 20. The composition according to claim 1, wherein thepigment particles are separated from each other by the calcium carbonatestructures in such a way that the distance between them is on average atleast approximately 60 nm, preferably at least approximately 100 nm,most suitably at least approximately 120 nm.
 21. The compositionaccording to claim 1, wherein the thickness of the shell formed by thecalcium carbonate structures is on average at least approximately 30 nm,especially at least approximately 50 nm, most suitably approximately60-500 nm.
 22. The method of manufacturing the composition according toclaim 1, according to which method the pigment particles are combinedwith the calcium carbonate particles, wherein: the calciumdioxide-bearing aqueous slurry which comprises pigment particles isatomized into calcium dioxide-bearing gas in order to carbonate thecalcium hydroxide, and in turn to generate a pigment composition whichcomprises calcium carbonate, the amount of calcium hydroxide in theaqueous slurry is chosen in such a way that the percentage of calciumcarbonate in the pigment composition is equivalent to a predefinedweight percentage, and the calcium hydroxide is carbonated in order toprecipitate the calcium carbonate particles which are to be attached toeach other, and the carbonation is continued until essentially all ofthe calcium hydroxide has been converted into calcium carbonate.
 23. Themethod according to claim 22, wherein the method is carried out in asurplus of carbon dioxide.
 24. The method according to claim 22, whereinthe carbonation is continued until the pH value of the pigment slurry isessentially neutral, preferably without adding any separate acid. 25.The method according to claim 22, wherein the carbonation is carried outin several stages.
 26. The method according to claim 25, wherein theaqueous slurry, which is a result of the atomizing of the calciumhydroxide-bearing aqueous slurry into carbon dioxide gas and also theresult of the carbonation, is recovered and brought to furthercarbonation.
 27. The method according to claim 26, wherein the aqueousslurry is further carbonated by atomizing it once more into carbondioxide gas or by bubbling carbon dioxide gas into the slurry.
 28. Themethod according to claim 22, wherein the carbonation is carried outcontinuously in such a way that the aqueous slurry is dripped at leastonce.
 29. The method according to claim 22, wherein at least essentiallyall of the calcium hydroxide-bearing aqueous slurry is added into thecarbonation together with the pigment particles.
 30. The methodaccording to claim 22, wherein the calcium hydroxide-bearing aqueousslurry is added into the carbonation in stages.
 31. The method accordingto claim 30, wherein at least part of the calcium hydroxide-bearingaqueous slurry is free of pigments when it is fed into the carbonation.32. The method according to claim 31, wherein the weight ratio betweenthe light-scattering pigment and the calcium carbonate is adjusted tothe desired ratio by choosing the amounts of the calcium hydroxide andcalcium carbonate in the aqueous slurry of the carbonation in such a waythat the percentage of calcium carbonate in the final pigmentcomposition corresponds to a predefined weight percentage.
 33. Themethod according to claim 22, wherein pigment is added little by littleand possibly separate from the calcium carbonate.
 34. The methodaccording to claim 22, wherein the calcium hydroxide-bearing aqueousslurry, which comprises light-scattering pigment particles, is directedthrough a high energy mixing zone, in which zone the aqueous slurry isbroken up into drops or even into nebulous drops, and then dripped intoa carbon dioxide-bearing gas.
 35. The method according to claim 34,wherein the mixing zone comprises at least one impact mixer in which thecalcium hydroxide-bearing aqueous slurry which comprises pigments, isdripped into fine particles, liquid drops or particles of solids ormixtures thereof, by using rotor blades which rotate in oppositedirections or, in the same direction but at greatly differing speeds, orby using a rotor-stator combination.
 36. The method according to claim22, wherein dispersants, surface modifying agents or stabilising agentsor mixtures thereof are added into the aqueous slurry of calciumhydroxide.
 37. The method according to claim 22, wherein calciumcarbonate particles are precipitated in such a way that calciumcarbonate particles adhere to the surface of titanium dioxide particlesand carbonate so that they bind to other calcium carbonate particles, inwhich case essentially opaque and stable titanium dioxide-calciumcarbonate aggregates are generated, which are at least partly coveredwith calcium carbonate particles.
 38. The method according to claim 22,wherein the method is carried out at a temperature of approximately30-100° C., typically 50-80° C.
 39. The method according to claim 22,wherein the calcium hydroxide-bearing aqueous slurry of the titaniumpigment particles is at least essentially free of fibres.
 40. A paintcomposition which comprises pigment and binder, and conventionalmanufacturing materials and additives used in paints, wherein at least 1weight-% of the pigment comprises a composition according to claim 1.41. A coating material composition which comprises pigment and binder,and conventional manufacturing materials and additives used in coatingmaterials, wherein at least 1 weight-% of the pigment comprises acomposition according to claim
 1. 42. A filler composition whichcomprises pigment, and conventional manufacturing materials andadditives used in filler compositions, wherein at least 1 weight-% ofthe pigment comprises a composition according to claim
 1. 43. A polymercomposition which comprises thermoplastic polymer, into which pigmenthas been mixed, and possibly conventional manufacturing materials andadditives used in polymer compositions, wherein at least 1 weight-% ofthe pigment comprises a composition according to claim
 1. 44. A printingink composition which comprises pigment mixed into the liquid phase,binding agent, and possibly colour pigment and other manufacturingmaterials and additives used in printing ink compositions, wherein atleast 1 weight-% of the pigment comprises a composition according toclaim
 1. 45. The composition according to claim 40, wherein at least 5weight-% of the pigment comprises a composition, in which compositionthe light-scattering pigment is titanium dioxide.
 46. The compositionaccording to claim 45, wherein at least 20 weight-% of the pigmentcomprises a composition, in which composition the light-scatteringpigment is titanium dioxide.
 47. Use of a composition according to claim1 as a pigment in paint, in coating material composition in paper orcardboard, in filler composition in paper or cardboard, in plastic or inprinting ink.
 48. The use according to claim 47, wherein thelight-scattering pigment is titanium dioxide.